Aerogels are three-dimensional network of nanophase architecture composed of gas [usually air] and solid structure, with air [gas] to solid ratio of up to 99% by volume. Thus aerogels have high porosity, high specific surface area, and very low density. The entrapped motionless air [gas] in the pores is responsible for the high insulation [low thermal conductivity] of the aerogel materials. Aerogels can be made as large monolithic shapes, or micron/submicron size bodies, or any size and shape in between. The gas inside the aerogel nanostructures can be replaced [displaced] with other substances, such as, for example, pharmaceuticals, which then are released into the desired targets in a controlled manner.
Polyethylene is a non-polar material with many desirable properties. At ambient conditions, it is considered rather chemically inert, non-toxic, transitive of infrared [IR] radiation, outstanding electrical insulating properties, such that its dielectric constant, and power factor are almost independent of frequency and temperature. It has also desirable mechanical properties.
Research, conducted to explore the possibility of preparation of novel polyethylene only aerogel materials, managed to create a novel methodology to manufacture polyethylene aerogels, which included preparation of polyethylene aerogels using standard polyethylene polymers [low and medium molecular weight (MW)] as aerogel precursors. Research proceeded to further develop this material to comply with multiple specifications [including radiometric, mechanical, thickness, as well as several other requirements]. It was then realized that preparation of thin [2-3 mm] and ultrathin [0.5-0.9 mm] aerogel sheets (using the standard polyethylene polymers), which is necessary for packaging of electronics, compromised radiometric and mechanical properties of the aerogel sheet. To solve this shortcoming, the research efforts obtained high density [HDPE] and ultrahigh molecular weight [UHMW] polyethylene polymeric precursors and proceeded to develop polyethylene aerogel sheets from these precursors to meet all the specifications and performance requirements for electronics and sensors applications.
These newly developed polyethylene aerogels may be considered as a platform technology for many other applications, including thermal, cryogenic, and sound insulation; sound frequency modulation, computer electronics, wide band antennas, membrane separations, filtration, as well as controlled release of encapsulated substances. Several product specifications, and performance criteria, such as mechanical, radiometric, insulation, and suitability for packaging of electronics, were met with outstanding results.
Broad Statement
Polyethylene aerogels and aerogel fiber webs or fabrics (woven or non-woven) have a high degree of molecular alignment and interconnected fibers, which offer good mechanical strength and high porosity with open interconnected three-dimensional pore structure of the aerogel fibers. The high porosity of the aerogel fibers forming the web, offer a distinct advantage over solid fibers and fiber webs formed from polymer melts, or other non-gel form of polymer solutions. In this procedure, the polymer in solution is made into cross-linked gel with three-dimensional open pore structure before introducing it to the fiber web making process.
The polymer or copolymer aerogel may be a polyolefin, polyester, polyamide, etc. The polymer or copolymer aerogel may be in the form of a fiber, optionally twisted for form a yarn. A web of such fibers forms a fiber web or fabric.
The drawing will be described in greater detail below.